Emulsion polymerization is a known technique for making emulsions containing silicone polymers, and is explained in detail in numerous references in the prior art, the most notable of which are U.S. Pat. No. 2,891,920 (Jun. 23, 1959), U.S. Pat. No. 3,294,725 (Dec. 27, 1966), U.S. Pat. No. 4,999,398 (Mar. 12, 1991), and European Patent 0 459 500 B1 (Dec. 4, 1991), all of which are assigned to the same assignee as the present application.
According to the standard technique, the polymerization reaction involves the opening of cyclic polysiloxane rings using an anionic or a cationic catalyst in the presence of water. The anions and the cations act as a polymerization catalyst for such reactions by functioning to open the ring of the cyclic polysiloxane, and allowing it to form linear siloxane oligomers having terminal hydroxy groups. These oligomers then react with other oligomers by means of a condensation reaction, with the result that higher molecular weight polysiloxanes are formed. A surfactant(s) is generally used to stabilize the polysiloxane in the emulsion in the form of small sized droplets.
Most typically, the cyclic polysiloxane used in these ring opening reactions has a structure generally corresponding to the formula: ##STR2##
where n generally has a value of about 3-6, and R1 and R2 represent alkyl groups containing 1-6 carbon atoms. Some examples of these cyclic polysiloxanes are hexamethylcyclotrisiloxane (D.sub.3), octamethylcyclotetrasiloxane (D.sub.4), decamethylcyclopentasiloxane (D.sub.5), and dodecamethylcyclohexasiloxane (D.sub.6).
In contrast, the cyclic polysiloxane used in the reaction according to this invention is a cocyclic silicone having a structure generally corresponding to the formula: ##STR3##
where a and b each represent an integer having a value of 1-10; R3, R4, and R5 each represent an alkyl group containing 1-6 carbon atoms; and R6 represents a higher carbon atom containing alkyl group, i.e., C.sub.8 or higher, such as --(CH.sub.2).sub.7 CH.sub.3, --(CH.sub.2).sub.11 CH.sub.3, or --(CH.sub.2).sub.15 CH.sub.3. R6 it is noted may contain more than sixteen carbon atoms, if desired. For example, R6 could contain as many as thirty or more carbon atoms.
The reason the present invention is unique, therefore, is that by using such a cocyclic silicone one can prepare silicone polymers containing two or more dissimilar repeating units, without the necessity of adding other types of precursors to the reaction mixture, as in the case of prior art processes.